Measuring carbon dioxide in refrigeration applications

CO2, a widely used refrigerant in the early 20th century, was largely replaced by the chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants in the 1940s. The damaging effect of the CFCs and HCFCs on the ozone layer became evident in the 1970s. These compounds are also effective greenhouse gases contributing to the climate change. Consequently, a gradual phasing out has been taking place in order to replace these compounds in various applications.

The Montreal Protocol was opened for signatures in 1987 to phase out the ozone-depleting chemicals, including CFCs and HCFCs, resulting in nearly all countries joining the effort to protect the ozone layer. Simultaneous re-inventing of natural refrigerants has taken place.

Many factors promote the use of CO2 as a refrigerant. It is inexpensive and energy-efficient. In addition, it has good heat transfer properties and is compatible with most materials. The challenges related to process design, high operating pressures and downtime safety issues can be overcome with modern technology. From an environmental point of view, CO2 does not cause ozone depletion and has lower global warming potential than the traditional refrigerants. As a result, CO2 refrigeration has found numerous applications. in food and industrial processing, cold storages, food retail and transfer, and sports facilities. It is also emerging in car and residential air-conditioning.

Safety and system integrity are key issues

To ensure the safety of personnel in a CO2 refrigerated facility, CO2 transmitters should be installed in every human occupied space and as close to potential leakage points as possible.

McAlpine Hussmann Ltd. has experience of integrating Vaisala CARBOCAP® Carbon Dioxide GMT220 Series Transmitters as leak detectors in CO2 refrigeration applications. McAlpine Hussmann Ltd. provides solutions for the display and refrigeration needs of supermarkets and grocery stores throughout Australasia. "Safety and system integrity are key issues," says Rob Whitehead, Application Engineer from McAlpine Hussmann Ltd. in New Zealand. "Local codes state that any refrigerated space open to public access must have local leak detection and alarms. We decided to go a step further and alarm every refrigerated room as well as the plant room."

Vaisala sensors are accurate and durable

Rob Whitehead lists the requirements for CO2 transmitters: "The leak detector has to be sturdy, have a remote sensor and a display. It needs to be able to talk to the control and alarm system."

The Vaisala CARBOCAP® Carbon Dioxide Transmitters GMT221 and GMT222 are especially designed for harsh and humid environments. "The Vaisala system has allowed us the flexibility of mounting the detector units outside the refrigerated rooms at sufficient height to avoid the risk of mechanical damage," says Rob Whitehead.